Restorative Neurology and Neuroscience

Rats trained to traverse a narrow elevated beam were given a single intraperitoneal injection of either D-amphetamine, clonidine, L-phenylephrine, prazosin, yohimbine, or saline 24 h after ablation of the right sensorimotor cortex and tested for recovery of beam-walking (BW) ability to day 16 postsurgery. Clonidine, prazosin and L-phenylephrine did not significantly affect BW recovery. A 10 mg/kg dose of yohimbine significantly accelerated BW recovery, as did D-amphetamine (2 mg/kg). Since D-amphetamine and yohimbine both increase norepinephrine (NE) release and prior research has implicated NE but not dopamine in BW recovery, these data support the hypothesis that increased NE release benefits functional recovery in this model of cortical injury. However, a possible role of dopaminergic or serotonergic influences of D-amphetamine or yohimbine treatment cannot be ruled out. To investigate the role of the NE system in maintenance of recovery, animals recovered from BW deficits 18 days after injury were administered clonidine, prazosin, or yohimbine and retested on the BW task. Both the α₁-NE antagonist prazosin (2 or 4 mg/kg) and the α₂-NE agonist clonidine (0.1 or 0.4 mg/kg) produced a dose-dependent, transient worsening of BW performance. This reinstatement of deficits in recovered rats suggests that integrity of the α-NE system is necessary for maintaining functional recovery.

The projection of regenerating axons and the specificity of motor reinnervation were studied after repair of the transected rat sciatic nerve with Y-tunnelled silicone chambers. This geometry was used experimentally to face either the proximal tibial or peroneal fascicle with two distal fascicular options usually the distal peroneal and tibial fascicle. A 4 mm gap separated the proximal and distal fascicles. Four weeks after the repair, preferential motor reinnervation could be demonstrated and there were always more axons projecting towards the distal homonymous fascicle. In contrast, if the distal stumps were disconnected from the target no fascicle specific projection of axons was observed. This was true even if segments from the median and ulnar nerve were used to replace either the distal tibial or peroneal segments. It appeared as though the size and not the type of fascicle determined the number of attracted axons. The results suggest that there is no fascicle specific guidance of regenerating nerve fibers.

The outgrowth of neurites in neuronal cell cultures reflects the intrinsic capacity for neurite regeneration and morphological rearrangements after axotomy and in plasticity. The role of fast axonal transport in these neurite outgrowth responses has not been investigated. We have recently shown that sabeluzole (R58735), a new neuro-active compound increases fast axonal transport in cultures of hippocampal neurons. In rat hippocampal neurons, N4 neuroblastoma cells and adult rat dorsal root ganglion cultures, incubation with sabeluzole at an optimal concentration of between 0.1 μM and 0.5 μM enhances neurite outgrowth between 10 and 30%. The relative number of cells with neurite length greater than twice the cell body, is also increased dose-dependently. Time-dependent studies further indicate that the rate of neurite elongation is markedly enhanced during the first 24–48 h. This neurite enhancing effect of sabeluzole is discussed in relation to the enhancement of fast axonal transport.

Rats trained in an 8-arm radial maze were given electrolytic lesions of the dorsal hippocampus or sham operations. Within 24 h of surgery, approximately half of the rats in each groups began 14 daily oral treatments with the central calcium channel blocker, nimodipine. Retention testing began seven days after surgery. The untreated rats that received the larger hippocampal lesions did not relearn the maze within one month (2.5 times the preoperative mean number of days). The untreated rats that received the smaller lesions relearned within the allotted time but still showed clear deficits. Nimodipine improved the maze scores of the animals with the smaller lesions, but not those of the animals with the larger lesions. It was unclear whether nimodipine led to the sparing of more cells in the hippocampal region, or whether spared-but-affected cells were returning to normal modes of functioning more rapidly in the group with the smaller lesions. These findings suggest that spared hippocampus was mediating behavior, and extend previous findings from this laboratory showing that nimodipine can enhance recovery of function on higher cognitive tasks after hippocampal lesions.

Human mesencephalic neurons from the second trimester have been cultured and characterised. Fresh, non-cultured cells were rounded and without processes post-dispersion but in culture differentiated with neurite outgrowth when treated with 2 mMdibutyryl cyclic AMP in the absence of serum. This morphological differentiation could be reversed by the addition of the serine protease, prothrombin. Immunocytochemical staining for dopamine, tyrosine hydroxylase, neuron-specific enolase and glial fibrillary acid protein, demonstrated that dopaminergic, non-dopaminergic and glial elements responded similarly. The conditioned medium contained quantifiable levels of catecholamines as measured by HPLC. These findings are relevant to both developmental neurobiology and clinical neural transplantation, evidencing the considerable plasticity and functional integrity of mesencephalic cells in the second trimester as well as the influence of environmental factors.

The effects of d-amphetamine on the recovery of aphasia following stroke was examined in 6 patients. Patients entered the study between 10 and 30 days post onset and were followed for 3 months. The Porch Index of Communicative Ability was used to project a 6 month recovery score. By 3 months post onset, 5 of the 6 patients obtained scores in excess of 100% of the 6 month projections.

PC12 cells grow in serum-free medium (SFM) if high doses of insulin (5–50 μg/ml), or combined insulin (5 μg/ml) and insulin-like growth factor-I (3 ng/ml) are added daily. Ganglioside GMl counteracts these effects in a dose-responsive fashion between 10 nM and 50 μM. This provides a serum-free system to study the interactive effects of gangliosides on growth and neuritogenesis in PC12 cells.